1. Field of the Invention
The present invention relates to a satellite broadcasting converter with high productivity and high performance.
2. Description of the Related Art
A conventional satellite broadcasting converter will be described below with reference to FIGS. 7 to 10.
Referring to FIG. 7, a box-shaped metal housing 21, a cylindrical metal waveguide section 22, and a funnel-shaped metal horn section 23 are integrally formed by die casting using aluminum.
A circuit section (not shown) for receiving satellite broadcast waves, such as an RF circuit, is contained inside the housing 21, and cables are connected to a plurality of connectors 24 attached to the housing 21 so as to lead received waves indoors.
As shown in FIGS. 8 and 9, a converting portion 22b, formed of a nearly trapezoidal projection, projects from an inner surface 22a of the waveguide section 22 toward the center.
Circularly polarized waves are converted into linearly polarized waves by the converting portion 22b, and are input the satellite broadcast wave receiving circuit section.
Next, a description will be given of a method of producing the waveguide section 22 and the horn section 23 for the conventional satellite broadcasting converter.
As shown in FIG. 10, first, a columnar mold 31 for forming the inner surface of the hollow waveguide section 22 is placed to abut on a truncated conical mold 32 for forming the inner surface of the horn section 23 and a part of the inner surface of the waveguide section 22.
In this case, recesses 31a and 32a for defining the projecting converting portion 22b are formed in the abutting portions between the molds 31 and 32, which allows the mold 31 and the mold 32 to be pulled out in the directions of the arrows X and Y, respectively, after molding.
Moreover, a plurality of split molds 33 for forming the outline of the waveguide section 22 and the horn section 23 are placed to define a space portion 34 between the molds 31, 32, and 33, where the waveguide section 22, the converting portion 22b, and the horn section 23 are to be formed.
Subsequently, molten aluminum is injected in the space portion 34. When the aluminum has solidified, the mold 31 is pulled out in the direction of the arrow X, the mold 32 is pulled out in the direction of the arrow Y, and the molds 33 are removed, whereby the production of the waveguide section 22 and the horn section 23 is completed.
Since the converting portion 22b projects from the inner surface of the waveguide section 22 in the conventional satellite broadcasting converter, the production of the converter requires the mold 31 for forming the inner surface of the waveguide section 22, and the mold 32 for forming the inner surface of the waveguide section 22 and the inner surface of the horn section 23. This increases the number of molds, and therefore, increases the cost. Moreover, since the molds 31 and 32 must abut on each other, they suffer serious abrasion damage, and the service life thereof is shortened.
Furthermore, since the molds 31 and 32 must abut at the projecting converting portion 22b, burrs are formed in the abutting portions therebetween, which deteriorates performance, and necessitates deburring.